1. Technical Field
This disclosure relates to a toner preparation method and apparatus, and a toner prepared thereby; and more particularly to a spray granulation method and a spray granulation apparatus for preparing a toner, and a toner prepared thereby.
2. Discussion of the Related Art
Developers for use in electrophotography, electrostatic recording and electrostatic printing, in their developing processes, are transferred to image bearers such as photoreceptors electrostatic latent images are formed on, transferred therefrom to a transfer medium such as a transfer paper, and fixed thereon. As the developers for developing electrostatic latent images formed on image bearers, a two-component developer including a carrier and a toner, and a one-component developer without a carrier, such as a magnetic toner and a nonmagnetic toner, are known.
Conventionally, as a dry toner for use in electrophotography, electrostatic recording and electrostatic printing, a pulverized toner is widely used, which is formed by kneading a toner binder such as styrene resins and polyester resins with a colorant, etc. upon application of heat, cooling the kneaded mixture to be solidified and pulverizing the solidified mixture.
Recently, polymerized toners prepared by suspension polymerization methods, emulsion polymerization condensation methods, etc. are being used. Besides, Japanese published unexamined application No. 7-152202 discloses a polymer solution suspension method of using a volume contraction. This method includes dispersing or dissolving toner constituents in a volatile solvent such as an organic solvent having a low boiling point to prepare a dispersion or a solution, emulsifying the dispersion or solution in an aqueous medium to form a droplet, and removing the volatile solvent. The diversity of resins this method can use is wider than those of the suspension polymerization methods and emulsion polymerization condensation methods, and has an advantage of being capable of using a polyester resin effectively used for full-color images requiring transparency and smoothness.
However, in the polymerization methods, since a dispersant is basically used in an aqueous medium, the dispersant impairing the chargeability of a toner remains on the surface thereof, resulting in deterioration of environmental resistance. In addition, a large amount of water is needed to remove the dispersant, resulting in unsatisfactory methods of preparing a toner.
Japanese published unexamined application No. 57-201248 discloses a spray dry method having been known from long ago as a method of preparing a toner without using an aqueous medium. This atomizes and discharges a toner constituent solution or a toner constituent liquid with various atomizers, and dries to form particles. Therefore, this does not have problems o using an aqueous medium.
However, particles prepared by the conventional spray granulation methods are coarse and large, and have a wide particle diameter distribution, resulting in deterioration of toner properties themselves.
Japanese Patent No. 3786034 discloses a method and an apparatus forming a microscopic droplet with a piezoelectric pulse, and drying and solidifying the microscopic droplet to form a toner. Further, Japanese Patent No. 3786035 discloses a method of forming a microscopic droplet with a heat expansion in a nozzle, and drying and solidifying the microscopic droplet to form a toner.
However, each of Japanese Patents Nos. 3786034 and 3786035 discharges a droplet only from one nozzle with one piezoelectric body, and the number of the droplets dischargeable per unit of time is small, resulting in poor productivity.
The present inventors disclose in Japanese published unexamined application No. 2006-293320 that a nozzle is oscillated by expansion and contraction of a piezoelectric body as an oscillator to discharge a toner constituent fluid droplet at a constant frequency, and that the droplet is solidified to from a toner. Japanese published unexamined application No. 2006-297325 discloses that an oscillator oscillating a discharge member having a discharge hole as an oscillation member with at a predetermined frequency such that a droplet is discharged from the discharge hole, and that the droplet is dried and solidified to from a toner.
However, as disclosed in Japanese published unexamined application No. 2006-293320, the piezoelectric body facing an periphery of the nozzle oscillates by expansion and contraction only a region of the nozzle facing an opening of the piezoelectric body, and therefore the nozzle is unable to have a large amount of displacement. Namely, the nozzle is likely to be clogged when discharging a toner constituent liquid having a high viscosity such as 10 mPa·s and including a large amount of dispersed solid contents. Therefore, the nozzle is still insufficiently formed to stably and efficiently prepare a toner. Although Japanese published unexamined application No. 2006-297325 discloses that a piezoelectric body oscillates the discharge member, a specific constitution is not disclosed therein and is not beyond the specification in Japanese published unexamined application No. 2006-293320.
Because of these reasons, a need exists for a nozzle formed of a member displaceable at a large amount of displacement.